Industrial waste products, such as waste chemicals, waste oil and so on are often of very high viscosity and heavily contaminated with wearing particles in varying size. When pumping these media it is important to use a low speed pump as possible, which can swallow large particles and to give the high viscous medium good time to flow up.
Today among others so called modified archimedes screw pumps are used, with a multiple toothed radially positioned sealing and pressure build-up disc, which is in engagement with the screw. An example on such screw pump is described in SE-B-8101863. Because of the geometry of the sealing disc the meshing part of the screw can not simply be machined, which implies bad sealing and high wear on included parts. The displacement is limited by screw flanks during one screw turn and the cylinder wall and two successive teeth on the sealing disc. In practice the whole screw diameter cannot be used, since the screw must have a supporting center shaft, which steals a part of the displacement of the pump. Moreover the relatively large sealing disc demands large space, which results in the pump being bulky.